TW201522534A - Aqueous primer composition for enhanced film formation and method of using the same - Google Patents

Abstract

A water-based bonding primer composition and a method of applying the same onto a metallic surface prior to adhesive bonding. The bonding primer composition is a water-based dispersion containing water, one or more epoxy resins, one or more curing agents, a silane compound, a low amount of propylene carbonate (PC), and optional additives. The bonding primer composition can form substantially smooth films by spraying, and at the same time, meet environmental regulations and provide high bonding performance.

Description

Aqueous primer composition for enhancing film formation and method of use thereof

In the manufacture of composite structures, especially in the aerospace and automotive industries, it is common to use a structural adhesive to bond the fabricated metal structure to a metal or composite bond or to pre-impregnate one or more of the resin-impregnated fibrous reinforcement. The body layup is laminated to the fabricated metal structure. Bonding typically requires curing of the structural adhesive after structural bonding. In general, to ensure maximum adhesion, carefully clean the dirt, soil, grease, and metal oxides from the metal surface just prior to bonding. Unfortunately, this procedure is often not used multiple times because cleaning and bonding operations are usually separated by longer downtimes. During these periods, the metal surface may hydrolyze, thereby reducing the adhesion strength of the bond. A solution to overcome this difficulty is to apply a primer to the cleaned metal surface.

Conventional primers are usually prepared by dissolving a thermosetting resin such as acetone, isopropanol, tetrahydrofuran (THF), methyl ether ketone, ethylene glycol, xylene, toluene, etc., in a volatile organic solvent. Ethyl acetate and the like. The solvent based primers form a smooth film when sprayed onto the metal surface prior to curing. However, the use of primers containing large amounts of volatile organic compounds ("VOC") is subject to increasingly stringent scrutiny for both toxicological and environmental reasons. Therefore, the primer based on water has become more and more desirable. However, commercially available water-based adhesive primers containing epoxy resins tend to form a powdery (powdered) coating when applied via a spray, and the resulting air dried film has poor scratch or abrasion resistance prior to curing. . If the primer is scraped off before curing, the structural bond can be problem. The scratch or abrasion resistance is related to the ability of the primer film to resist scratching or abrasion (i.e., removal by friction) during air drying after handling the metal component having the undercoat film thereon.

Another important consideration in the use of primers is the durability and corrosion resistance of the joint formed between the metal surface and the material bonded to the metal surface. This is especially important in structural applications, such as aircraft structures, due to the exposure of such joints to a wide range of environmental conditions with extreme temperatures, high humidity, and high corrosive marine environments. In order to avoid joint failure and meet strict commercial passenger and cargo standards, adhesives bonded to structural components must withstand harsh environmental conditions and, in particular, corrosion and dissolution in wet, salty environments, especially Such as those derived from marine droplets or de-icing materials. Failure of such joints typically begins with water diffusing through the adhesive and then corroding the underlying metal structure.

There is still a need in the art for a method of bonding a metal structure using a primer formulation that can form a substantially smooth film by spraying while meeting environmental regulations to provide high adhesion and corrosion protection.

Disclosed herein is a method of applying a one-part water-based adhesive primer composition to a metal surface of a first substrate and then bonding the metal surface to a second substrate via a curable adhesive. The adhesive primer composition is a water-based dispersion containing water, one or more epoxy resins, one or more curing agents, a decane compound, a small amount of propylene carbonate (PC), and optional additives.

1A is a photographic image showing the surface of a primer film formed from a formulation containing propylene carbonate according to an embodiment.

Figure 1B is a photographic image showing the surface of a primer film formed from a solvent-free control formulation.

Figure 2 is a photographic image showing the surface of a primer film formed from a formulation containing propylene carbonate according to another embodiment.

The adhesive undercoating compositions of the present invention provide corrosion protection and enhanced adhesion to metallic materials, particularly aluminum and aluminum alloys used in the aerospace industry. The presence of propylene carbonate has been found to enhance film formation of the primer composition by enabling the formation of a smooth undercoat film that is scratch resistant and resistant to rubbing prior to curing and resistant to solvent wiping after curing. Additionally, propylene carbonate can be stabilized and provide a neutral pH (about 7 ± 0.5) by reacting with certain water soluble curing agents/catalysts in the primer composition to act as a buffer. Some water soluble curing agents and catalysts (e.g., imidazole) tend to dissolve in the water based primer composition to form a solution having a high alkaline pH, thereby negatively affecting the adhesion of the primer film to the metal surface. Therefore, the propylene carbonate is a multifunctional component in the primer composition.

One aspect of the present invention relates to a method of applying a water-based adhesive undercoating composition to a metal surface of a first substrate and then bonding the metal surface to a second substrate. The adhesive primer composition is a water-based (or aqueous) dispersion having a solid content of 10% to 25% and containing water, one or more thermosetting resins, a curing agent/catalyst, a decane compound, and a small amount of propylene carbonate. Ester (PC). The amount of PC is less than 15 wt.% (wt%), preferably from 1 wt.% to 10 wt.%, based on the weight percent of the total weight of the composition. In some embodiments, the amount of PC can be from about 10-15 g/L of a water based primer composition. The bonded primer composition can be applied to the metal surface by spraying to form a smooth, continuous primer film. The term "smoothing" in this context refers to a film having a flat surface that is substantially free of appreciable protrusions, clumps or indentations and that does not have a powdery appearance. Alternatively, the spray-primed film can be air dried at ambient temperature (21 ° C to 26 ° C) for 30 minutes or less, for example 15-30 minutes. Due to the low loading of PC, the primer composition is easy to comply with current OSHA (Occupational Safety and Health Administration) and REACH (Registration, Evaluation and Restriction Act (Registration, Evaluation) , Authorization and Restriction of Chemicals)). current In the United States, propylene carbonate is considered a non-VOC chemical compound.

For adhesive bonding of a metal substrate to another substrate (metal or composite substrate), the water-based primer composition of the present invention can be applied to a metal surface by spraying or brushing to form a curable undercoat film. After drying at ambient temperature for less than 30 minutes, the curable primer film is scratch resistant and rubbed off. Preferably, the metal surface is pretreated prior to application of the primer composition to enhance adhesion of the metal surface to the subsequently applied primer film and to provide corrosion resistance to the metal surface. The primer film is cured in an oven at elevated temperature (for example, at 250 °F or 350 °F for 1 hour) and then bonded to the assembly. The undercoat surface of the metal substrate is then adhered to the second substrate by providing a curable, polymer-adhesive film between the undercoat surface and the second substrate. The second substrate may be another metal substrate or a composite substrate composed of reinforcing fibers embedded in or impregnated with the matrix resin. The adhesive may be applied to the surface of the second substrate, or alternatively, an adhesive may be applied to the undercoat surface of the first substrate. The resulting assembly is then subjected to curing at elevated temperatures to cure the adhesive and thus create an adhesive structure. Curing can be carried out by applying heat and pressure to the assembly. The primer composition is formulated to be compatible with conventional curable, polymeric adhesives (especially based on epoxide adhesion) which are curable at temperatures ranging from 250 °F to 350 °F (121 °C to 177 °C) Agent) compatible.

The term "substrate" as used herein includes layers and structures of any shape and configuration.

The term "cure and curing" as used herein refers to the hardening of a polymeric material by cross-linking of a polymer chain by chemical additives, ultraviolet radiation or heat. "Curable" materials are capable of curing, ie becoming hardened.

When the second substrate is a composite substrate composed of a reinforcing fiber and a matrix resin, the matrix resin may be partially or completely cured or uncured. When the matrix resin is uncured or only partially cured before the adhesive is joined to the two substrates, complete curing of the matrix resin and curing of the adhesive are simultaneously performed during the bonding phase.

The primer composition can be applied (eg, by spraying) to the metal surface in several layers until The desired film thickness. For example, the amount of primer composition applied should be such that the cured basecoat film can have a thickness of from about 0.0001 inch to about 0.0003 inch (or 0.1 mil to 0.3 mil).

The water-based primer compositions disclosed herein preferably comprise an inorganic or organic corrosion inhibitor to further improve long-term corrosion resistance.

To enhance adhesion of the metal surface to the subsequently applied polymeric primer film, the metal surface can be pretreated prior to application of the primer composition thereto. Suitable surface treatments include wet etching, anodization (e.g., phosphoric acid anodization (PAA) and phosphoric acid/sulfuric acid anodization (PSA)) and sol-gel processes known to those skilled in the art. A more specific example of a suitable surface treatment is ASTM D2651, which comprises cleaning with a soap solution followed by wet etching and then anodizing with an acid. The water-based primer compositions disclosed herein are formulated to be compatible with the various surface treatments.

PAA typically involves the use of phosphoric acid (e.g., ASTM D3933) to form a metal oxide surface, and PSA typically involves the use of phosphoric acid-sulfuric acid to form a metal oxide surface. Anodic treatment produces a porous, rough surface into which the primer composition can penetrate. Adhesion is primarily due to mechanical interlocking between the rough surface and the undercoat film.

The sol-gel process typically involves the growth of a metal-oxyl polymer via hydrolysis and condensation of an aqueous solution of an organofunctional decane with a zirconium alkoxide precursor to form an inorganic polymer network on the metal surface. The sol-gel coating provides good adhesion between the metal surface and the subsequently applied primer film via covalent chemical bonding.

Thermosetting resin

A preferred thermosetting resin is an epoxy resin. Suitable epoxy resins comprise a polyfunctional epoxy resin having at least about 1.8 functional groups or at least about 2 functional groups. The epoxy resin is a solid glycidyl ether which is optionally extended by a chain, such as resorcinol and bisphenol (e.g., bisphenol A, bisphenol F, and the like). Also suitable are aromatic amine-based solid amine and the phenol glycidyl derivatives, for example N, N, N ', N ' - tetraglycidyl-4,4 '- diamino diphenyl methane. Further, the epoxy resin may have an epoxy equivalent weight (EEW) of about 145 to 5,000, and preferably about 300 to 750 equivalents, and the equivalent of 325 is optimal.

The epoxy resin can be in the form of a solid or a dispersion of a solid epoxide. The epoxy resin in a dispersed phase may be a dispersion of one or more epoxy resins in the form of a mixture of different particles, or may be composed of only one type of particles containing more than one epoxy resin per particle. Thus, a flexible epoxide (eg, a higher molecular weight bisphenol A or bisphenol F epoxide) and a high temperature resistant epoxide (eg, tetraglycidylmethylene bisaniline (TGMDA)) may be blended, The mixture is then cooled, ground or otherwise dispersed into solid particles of the desired size. These same epoxy resins can advantageously be dispersed separately without being blended.

Mixtures of different epoxy resins can be used. In one embodiment, the epoxy resin mixture comprises a novolac epoxy resin and a bisphenol A diglycidyl ether ("DGEBA") resin. Examples include novolac epoxy resins (e.g., Epirez 5003 available from Huntsman) and bisphenol A epoxy resins (e.g., XU-3903 available from Huntsman and D.E.R. 669 available from Dow Chemical Company). In another embodiment, the resin mixture contains an epoxy resin having a functional group of about 4 or less and an epoxy resin having a functional group of about 5 or greater. It is preferred to use a lower amount of epoxy resin (i.e., an epoxy resin having a functional group of 5 or greater) based on a minimum amount (e.g., less than 40 wt.% based on the sum of all epoxy resins in the composition). It has been found that the use of such minimum amounts of such higher functional epoxy resins increases the solvent resistance of the cured primer composition without substantially impairing the adhesive properties.

In one embodiment, the primer composition comprises a mixture of the following epoxy resins: 1) 30 wt.% to 70 wt.% of an epoxy having a functional group of from about 1.8 to about 4 and an epoxy equivalent weight of from about 400 to about 800. Resin; 2) from 5 wt.% to 20 wt.% of an epoxy resin having a functional group of from about 1.8 to about 4 and an epoxy equivalent of from about 2,000 to about 8,000; and 3) from 10 wt.% to 40 wt.% of the functional group is An epoxy resin of about 5 or greater and having an epoxy equivalent weight of from about 100 to about 400, The weight percentage is 100% in total based on the total weight of the epoxide mixture.

The total amount of epoxy resin may be from about 20% to about 60% by weight based on the total weight of the primer composition.

Curing agent and catalyst

The water-based primer composition contains one or more curing agents and/or catalysts which are water-soluble or water-insoluble. Suitable curing agent comprises water-soluble amine-substituted three , for example, 2-β-(2 ' -methylimidazolyl-1 ' 1-ethyl-4,5-diamino-s-three (It is commercially available as CUREZOL 2 MZ-Azine®); modified polyamines such as Ancamine 2014®; dicyanodicimide (DICY) or water insoluble curing agents, such as diurea based curing agents (eg 24) or from CVC Chemicals of toluene Omicure -2,4- bis (N, N '- dimethylurea) (e.g. from CVC Chemicals of Omicure U-24); amine - epoxide adducts and / or aromatic Aminamines such as bis(3-aminopropyl)-hexahydropyridyl (BAPP) (purchased from BASF).

The catalyst may be added as an optional component to accelerate the curing/crosslinking of the thermosetting resin or to enable curing at a lower temperature. The solid water dispersible catalyst can be added to effect curing of the primer composition when the particular curing agent does not have sufficient activity at the heating temperature of the primer composition. For example, when the curing agent is active at 350 °F, a catalyst is added to enable curing at about 250 °F. The catalyst may be water soluble or water insoluble and may be in the form of particles having a particle size such that substantially 100% of the particles have an average diameter of less than about 30 μm. The average diameter of the particles can be measured by means of a laser diffraction method using instruments such as Malvern Mastersizer 2000 and Horiba LA-910. Typical catalysts that may be employed include, but are not limited to, diurea, blocked imidazole, substituted imidazole or other blocked amines (e.g., amine/epoxide adducts, hydrazine, etc.).

The curing agent alone or in combination with one or more catalysts may be present in an amount of from about 2 parts to 30 parts per 100 parts of epoxy resin (i.e., the total amount of epoxide).

Decane compound

The decane compound in the water-based primer composition has a decane functional group that can react or bond to the material to be bonded to the metal surface. Suitable decane compounds comprise organodecane. The organic decane having a hydrolyzable group is preferred. In certain embodiments, the organodecane has the general formula:

Wherein n is greater than or equal to 0; wherein each X is OH, OCH ₃ and OCH ₂ H ₅ ; wherein R ₁ is CH=CH ₂ ,

Or CH ₂ -CH ₂ -CH ₂ -Y, wherein Y is NH ₂ , SH, OH, NCO, NH-CO-NH ₂ , NH-(CH ₂ ) ₃ NH ₂ , NH-aryl, or And each of R ₂ is alkyl, alkoxy, aryl, substituted aryl or R ₁ .

Examples of suitable commercially available organodecane compounds are those available from OSi Specialties, Inc., Danbury, Conn, including but not limited to A-186, β-(3,4-epoxycyclohexyl)ethyltrimethoxy Base decane; A-187, γ-glycidoxypropyltrimethoxydecane; A-189, γ-mercaptopropyltrimethoxydecane; A-1100, γ-aminopropyltriethoxydecane; A-1106, aminoalkyl polyoxyl solution; A-1170, bis-(γ-trimethoxy-oxime Alkyl)amine; Y-9669, N-phenyl-γ-aminopropyl-trimethoxydecane; Y-11777, aminoalkyl polyoxyl/water solution; and Y-11870, epoxy functional group A solution of decane. Other suitable commercially available organodecanes include, but are not limited to, Z-6040, gamma-glycidoxypropyl-trimethoxydecane from Dow Corning, Midland, Mich., HS2759, aqueous epoxy functional decane; HS2775, An aqueous solution of amino decane; and HS 2781, an aqueous solution of an oxirane having an amine group and a vinyl group, all sold by Huls America, NJ. Another example is 3-glycidoxypropyl methoxy decane sold under the trademark Z-6040.

Typically, the organodecane is present in the water-based primer composition in an amount ranging from about 0.01 parts to 15 parts per 100 parts water, preferably from about 0.1 parts to 10 parts per 100 parts water.

The organodecane may be in the form of a liquid or powder that can be added directly to the water based primer composition.

Corrosion inhibitor

Chromate or non-chromate corrosion inhibitors can be used in the water-based primer compositions disclosed herein, however, non-chromate compounds are preferred for compliance with environmental, health and safety regulations. Examples of suitable chromate corrosion inhibitors include barium chromate, barium chromate, zinc chromate, and calcium chromate. The non-chromate corrosion inhibitor comprises an inorganic compound containing one or more ions selected from the group consisting of NaVO ₃ , VO ₄ , V ₂ O ₇ , phosphates, phosphonates, molybdates, hydrazines, and borates. . Examples of inorganic, non-chromate corrosion inhibitors include, but are not limited to, metavanadate anions such as sodium metavanadate, combinations of molybdate and metavanadate or molybdate, metavanadate, phosphoric acid Any combination of salts, phosphonates, hydrazines, and borates. Also suitable are organic corrosion inhibitors, including those that are chemically anchored to the surface of the particles or encapsulated and released in a corrosive environment. Examples of such releasable organic corrosion inhibitors are set forth in U.S. Patent Application Publication No. 2010/0247922, issued Sep. 30, 2010. A combination of different corrosion inhibitors can be used.

The total amount of corrosion inhibitor may range from 1 to 7 wt.%, based on the total weight of the primer composition.

Optional additive

The water-based primer composition may optionally contain conventional dyes, pigments, and inorganic fillers. The total amount of such optional additives is less than 3 wt.%, such as from 0.1 wt.% to 2 wt.%. A benefit of compositions containing dyes or pigments is that surface coverage can be more easily assessed by visual methods. An inorganic filler in particulate form is added to control the rheology and stability of the application process. Suitable inorganic fillers include fumed cerium oxide, clay particles and the like.

According to one embodiment, the water-based primer composition is a sprayable dispersion having a pH of 6-8 and containing: (i) 20-60 wt.% of one or more epoxy resins; (ii) alone or in contact with a total of 2-30 parts of curing agent per 100 parts of epoxy resin; (iii) organic decane in an amount of 0.1 parts to 10 parts per 100 parts of water; (iv) 1-10% by weight of propylene carbonate; (v) 1-7 wt.% of at least one chromate or non-chromate corrosion inhibitor; (vi) 0.1-2 wt.%, as the case may be, inorganic filler and/or pigment/dye in particulate form; (vii Water to provide 10% to 25% solids, wherein "wt%" represents the weight percent based on the total weight of the composition.

Instance

The following examples show the performance results obtained using a water-based adhesive primer formulation containing a small amount of propylene carbonate compared to other primer formulations that do not contain propylene carbonate.

Example 1

The primer formulations were prepared according to the formulations disclosed in Table 1.

The pH of the primer formulation in Table 1 was about 6.5.

Each primer formulation was sprayed onto a surface treated Al-2024 alloy using a HVLP (High Speed Low Pressure) gun to form a film having a thickness of 0.2 mils. The surface treatment is performed in accordance with ASTM D 2651, which includes cleaning, FPL etching, and PAA anodization. The resulting uncured film was dried by air at ambient temperature. For comparison, a control primer film was formed by the same method using a solvent-free formulation (PC-free formulation 1).

The undercoat film was evaluated and the results are shown in Table 2.

For film drying time, "passing" means that the film is dried by air at ambient temperature for less than 30 minutes after spraying, and "failed" means that it takes too long or more than 30 minutes to dry after spraying.

The scratch resistance test involves rubbing the air dried, uncured film by hand or rubbing the surface of the film with a dry white cloth to see if any of the film materials are attached to the cloth after several times of rubbing.

The surface of the air-dried, uncured base film formed from Formulation 1 was found to be smooth and scratch resistant and is shown in Figure 1A (photographic image of the undercoat surface). In contrast, the air dried, uncured control film had a powdery appearance as shown in Figure 1B and did not pass the scratch resistance test. The uncured base film formed from Formulation 2 took too long, more than 30 minutes to dry after spraying at ambient temperature, and did not pass the scratch resistance test.

Example 2

Primer formulations were prepared according to the formulations disclosed in Tables 3, 4 and 5.

Each primer formulation was sprayed onto a surface treated Al-2024 alloy using a HVLP gun to form a film having a thickness of 0.2 mils, as discussed in Example 1. For comparison, A control primer film was formed by spraying a primer formulation containing no solvent (no propylene carbonate-containing formulation 3).

The air dried, uncured base film was evaluated and the results are shown in Table 6. The pH of the primer formulation is also shown in Table 6. In addition, a one-sided tensile shear test (ASTM D1002) and a floating roll peeling (ASTM D3167) test were performed to determine the adhesion properties of the undercoat film. The tests were carried out by bonding the undercoat surface to another aluminum alloy (Al 2024T3) plate using an epoxide-based curable adhesive (FM 73M from Cytec Industries, Inc.) and then curing. Table 6 shows the results of the mechanical test.

The air-dried, uncured basecoat film formed from Formulation 3 is uniform and smooth and exhibits good scratch resistance. Figure 2 shows the surface of the undercoat film formed from formulation 3. In contrast, the uncured control film was powdery in appearance and had poor scratch resistance. In addition, the pH of the control formulation (without propylene carbonate) was about 9.2 due to the presence of the water-soluble catalyst 2-β-(2 ' -methylimidazolyl-1 ' 1-ethyl-4 ,5-diamino-s-three . By the addition of propylene carbonate, the pH of Formulation 3 can be effectively reduced to about 7, just at the desired neutral level. Here, propylene carbonate functions not only as a film promoter but also as a buffering agent which reacts with a water-soluble catalyst to bring the pH of the primer composition from alkali to about 7.

Although formulations 4-8 were able to form a smooth film by spraying, the films did not provide the desired bonding properties due in part to the high pH. In addition, the formulation 4 takes too long to dry. It has been found that a water based primer neutral pH can be used to optimize surface adhesion with a decane coupling agent and is typically necessary for the overall balance performance of a water based primer.

Claims (19)

A surface treatment for treating a metal surface prior to bonding of the adhesive, comprising: applying a water-based primer composition to the metal surface to form a curable undercoat film having a smooth, continuous surface, the water-based bottom The coating composition comprises: one or more epoxy resins; at least one curing agent; a decane compound having at least one hydrolyzable group; propylene carbonate; and water, wherein the water-based primer composition has 10% to 25% The solids content of %, and the amount of propylene carbonate is less than 15% by weight based on the total weight of the primer composition. The surface treatment of claim 1 wherein the water-based primer composition is applied by spraying. The surface treatment of claim 1, wherein the pH of the primer composition is in the range of 6 to 8. The surface treatment of claim 1, wherein the curing agent is water soluble, and in the absence of propylene carbonate, the pH of the primer composition will increase. The surface treatment of claim 1, wherein the undercoat film is air dried at ambient temperature (21 ° C to 26 ° C) for 30 minutes or less. The surface treatment of claim 1, wherein the water-based primer composition further comprises a corrosion inhibiting compound. The surface treatment of claim 1, wherein the metal surface is a surface of an aluminum or aluminum alloy substrate. The surface treatment of claim 1, wherein the metal surface is subjected to anodization or sol-condensation A gum process to form a metal oxide coating prior to application of the water based primer composition. A metal surface having a primer film produced by surface treatment as claimed in claim 1. A bonding method comprising: (a) applying a water-based primer composition to a surface of a metal substrate to form a curable undercoat film having a smooth, continuous surface, the water-based primer composition comprising: Or a plurality of epoxy resins; at least one curing agent; a decane compound having at least one hydrolyzable group; propylene carbonate; and water, wherein the water-based primer composition has a solid content of 10% to 25%, and The amount of propylene carbonate is less than 15% by weight based on the total weight of the primer composition; (b) bonding the metal substrate to the second substrate in an adhesive manner, thereby allowing the curable, polymer adhesive to be located at the bottom Between the coated film and the second substrate; (c) curing the adhesive to form an adhesive structure. The bonding method of claim 10, wherein the water-based primer composition is applied by spraying in the step (a). The bonding method of claim 10, wherein the water-based primer composition further comprises a corrosion-inhibiting compound. The bonding method of claim 10, wherein the second substrate is another metal substrate. The bonding method of claim 10, wherein the second substrate is formed of aluminum or an aluminum alloy. The bonding method of claim 10, wherein the second substrate comprises a resin matrix and is strong Composite substrate of chemical fiber. The bonding method of claim 15, wherein the composite substrate is uncured when attached to the metal substrate in the step (b). The bonding method of claim 15, wherein the composite substrate is partially or completely cured when attached to the metal substrate in the step (b). A water-based primer composition having a pH in the range of 6 to 8 and sprayable, the primer composition comprising: (i) 20 wt.% to 60 wt.% of one or more epoxy resins; (ii) a total of 2 parts to 30 parts of curing agent per 100 parts of epoxy resin, alone or in combination with one or more catalysts; (iii) an organic decane in an amount of 0.1 parts to 10 parts per 100 parts of water; (iv) 1 wt.% to 10 wt.% propylene carbonate; (v) 1 wt.% to 7 wt.% of at least one chromate or non-chromate corrosion inhibitor; and (vi) water to provide 10% to 25 %solid. The water-based primer composition of claim 18, further comprising 0.1 wt.% to 2 wt.% of an additive selected from the group consisting of inorganic fillers in the form of microparticles, pigments, dyes, and combinations thereof.